Hot Water Extraction Processes.
The use of hot water extraction of proanthocyanidins from biological material is covered extensively in the prior art. Examples of discussions of such techniques are in the examples below, along with the attendant problems, even if the method claimed in the patent is not solely a hot water extraction technique. Non-bark materials: Japanese Patent Application No. 62101976 (Publication Number 63267774A) reveals that it is possible to obtain a solution of proanthocyanidins derived from the juice of apples, grapes and other fruit, soy beans (etc). U.S. Pat. No. 4,981,688 (Ayroles) discloses extraction of proanthocyanidins from ginko biloba leaves using aqueous ketone solvents. U.S. Pat. No. 5,607,965 (Kando) discloses extraction from a grape extract. U.S. Pat. No. 5,532,012 (Balentine) discloses an extractive from tea. Tree bark materials: The most common bark discussed is that of Pinus radiata bark. However other species of bark or tree have been used for extraction of proanthocyanidins. For example: Australian AU B 58998/80 uses Croton or a Calophyllum species as the starting material and the acacia species is used in NZ Patent No. 181274 (NZ Forest Products).
The extractives of Pinus radiata bark (both inner and outer) have been well documented. For example, Markham and Porter in New Zealand Joumal of Science (1973, Vol 16, p. 751) detail the phenolic compounds which can be extracted with ethyl acetate solution, amongst others. These include procyanidins, high molecular weight condensed tannins and phenolic acid compounds.
A range of methods of hot water extraction of Pinus radiata have been proposed: Yazaki (Holzforschung 37 (1983) 87) reviewed hot water extraction of bark, followed by freeze drying, and dissolution in 10% aqueous sodium hydroxide solution. This was then subjected to micro-filtration and ultra-filtration. However, uniform quality of the extract was noted as a problem.
This process is similar to that disclosed in Australian Patent Application No. 57753/80 (CSIRO). Yazaki (Holzforschung 39 (1985) 79) reviewed the results of a similar process, using solvent solutions which obtained more reliable results. NZ Patent No. 179933 (NZ Forest Products) also noted the problem of uniformity of extract. In NZ Patent No. 234804 (Chem Eng Contracts) there is extensive discussion of the problems relating to hot water extraction processes. In NZ Patent No. 181274 hot water extraction is disclosed, but with a two stage control of the pH value of the extractive solution.
Another problem that has been noted with extraction processes of proanthocyanidins is that in some techniques there is degradation of the product as the proanthocyanidins starts reacting before the extraction process is completed. This is countered by control of the pH (for example: NZ Patent No. 181274, NZ Forest Products Ltd) or control by selection of solvent(s) used (for example, Yazaki 1985).
In summary, there are three problems relating to hot water extraction processes. Firstly, when only hot water extraction alone is used, high purity yield has been found to be too low for viability of the process commercially. Low yields are also noted from the yields disclosed in Japanese Patent Application No. 62101976 (Publication Number 63267774A). This patent discloses that it is possible to obtain a solution of high purity and yield by the treatment of a proanthocyanidin-containing solution (in 0.5% v/v alcohol) with ultra-filtration and/or reverse osmosis. However the yield disclosed in the examples given is 0.72% w/w or less of proanthocyanidins.
Second and thirdly, uniformity of quality is sometimes problematic. This may result from the selection of the size or type of material for the extraction process or from the proanthocyanidins reacting with chemicals present in the process and thus resulting in a degraded or less pure product.
An object of the present invention is the provision of a method of extraction for proanthocyanidins which overcomes the disadvantages of the known processes of purely hot water extraction and still produces a commercially acceptable yield of high purity of the proanthocyanidins. This object includes the avoidance of solvents other than water, and avoids the use of other chemical additives such as sodium hydroxide and sodium chloride for pH adjustment and salting down.